Old Units of Measurement

Units of length

• 1 yard = 3 feet    [1 yard is approximately 0.914 metres]
• 1 chain = 22 yards
• 1 chain = 100 links
• 1 link = 7.92 inches
• 25 links = 1 perch = 5.5 yards
• 1 rod = 1 perch = 1 pole = 25 links or 5.5 yards = 16 1/2 feet = 1/4 chain
• 1 furlong = 10 chains = 40 rods = 220 yards
• 1 mile = 8 furlongs = 80 chains
• 3 miles = 1 league
• 3 barleycorns = 1 inch

Units of area

• 1 acre = 1 chain x 1 furlong = 10 square chains = 4840 square yards
• 1 acre = 4 roods (= 0.404686 hectares)
• 1 rood = 1 furlong  x 1 rod = 40 square perches or square rods = 1210 square yards
• 1 square perch = 1 square rod = 30.25 square yards

Notes

Chains and links were named for surveying methods. Most of the other units were agricultural in origin. Furlong (aka furlough) meant furrow length. During the Middle Ages, an acre was the amount of land that could be ploughed in one day with a yoke of oxen (approximately!), and was one chain in width (22 yards), and one furlong (10 chains, or 220 yards) in length.

The land areas given in the 19^th Century tithe apportionments are given in acres, roods and perches. By perches they actually meant square perches. As above, there are 40 square perches in a rood and 4 roods in an acre.

Britain’s railways are still measured in miles and chains.

A cricket pitch is 1 chain (= 22 yards) long.

Recently (April 2022) we had an enquiry about a mid-19th century Australian land use document which showed rectangular and triangular plots of land. The sides of each plot were marked with a number somewhere between 100 and 212, and in the centre of each plot was a number like '0.0.22'. The enquirer was trying to understand what units were being used. It transpired that 0.0.22 indicated the land area in the same form as a tithe map, i.e. acres.roods.square perches; thus 0.0.22 meant 22 square perches. By calculating the areas of a few sample plots we were able to confirm that the linear dimensions of the sides of the plots were in links. 

JK